1. Field of the Invention
The present invention relates to a method of manufacturing a metallic film consisting of giant single crystal grains, and more particularly, to a method of manufacturing a metallic film consisting of giant single crystal grains on a substrate having no epitaxy relation to the metallic film to be deposited thereon.
2. Description of the Related Art
Recently, miniaturization of functional devices consisted of dielectric, piezo-electric, superconductive, and magnetic ceramic materials is becoming a world-wide tendency in order to meet the requirements of high-density integration, and functionality improvement of electronic ceramic parts or devices. For miniaturization of such devices comprised of ceramic thin film materials, single crystal materials such as silicon, MgO, SrTiO3, LaAlO3, and sapphire, and poly-crystal materials such as alumina and diamond have been used as a substrate.
The above thin film materials and devices are mainly formed on a metallic film, which acts as the electrode, for driving of the devices or for signal processing. It has been reported that the single crystalline metallic film can remarkably increase the physical and electrical properties of the thin films to be deposited thereon. Up to now, single crystalline metallic films have been grown on single crystal substrates. However, this case cannot completely avoid problems (for example, residual stress, delamination from the substrate, change of interface characteristic, or the like) caused by lattice mismatch between the film and the substrates. Also, when a oxide single crystal substrate such as MgO, SrTiO3, sapphire or the like is used instead of the substrate conveniently used such as Si wafer for the device fabrication, many problems occur during the integration of the devices.
Meanwhile, as a method of manufacturing bulk single-crystals of metal/non-metal materials a Czochralski growth, a floating-zone growth, or a melt-growth method is used. In case of the thin-film single crystal growth, a single crystal growth method for the bulk material cannot be used. Instead, a method using a epitaxial relation with the substrate is mainly used. In case of using the single crystal substrate, it is very important to have a lattice-matched substrate with that of the material to be grown thereon. If the difference between the lattice constants of the two materials is above about 15 percentages, the single crystal film cannot be grown.
As a result, in order to obtain a single crystal film, the kind of substrate is limited depending upon the deposited material. Furthermore, a limited deposition technique using expensive deposition equipment such as molecular beam epitaxy should be used, thereby increasing the production cost.
Meanwhile, in case of using the metallic film as a bottom electrode of various kinds of devices, its crystallographic characteristic has an profound effect on a preferred orientation or microstructure of the thin film material to be formed thereon, and this affects the characteristic of the manufactured devices. Specifically, when an oxide film is deposited on the metallic film, the nucleation of the oxide film occurs at grain boundaries or defect site of the metallic film having the lowest nucleation energy barrier. Accordingly, factors such as the existence/nonexistence of the grain boundary, density of the defects or the like of the metal lower electrode have an effect on the preferred orientation and microstructure of the oxide film, and this affects the physical property of the device. Accordingly, the crystallization and microstructure of the oxide film formed on the substrate can be controlled by regulating the orientation of the metallic film used as the electrode or substrate towards a specific crystallographic direction, and this can enhance the performance of the device. For the reason described above, many efforts to form a single crystal metallic electrode have been made by many researchers. Conventionally, a method using the single crystal substrate of MgO or Al2O3, or a method of forming an intermediate layer has been used. However, in case of method manufacturing any thin film device using a single crystal substrate such as MgO, it is not suitable for a silicon integrated circuit manufacturing process developed at present. Furthermore, processing of the substrate itself becomes difficult. Therefore, the use of the single crystal substrate, such as MgO, for manufacturing the device lacks practical application. In case of using the intermediate layer, the process is complicated, and the resultant metallic film is usually not of single crystalline, but is a film oriented in a certain direction, thereby limiting the control of the physical property of the oxide film. Accordingly, a method of forming giant metal grains, whose average grain size to thickness ratio is above 50 on a substrate having no epitaxy relation with the metal film is invented which has not been proposed yet.
FIG. 1A shows a conventional process of manufacturing a single crystal metallic film. It will be known from FIG. 1A that the epitaxial metallic film can be formed by depositing a metallic film 101 on a single crystal substrate 100 whose lattice mismatch is less than 15%.
In the above case, the material used as the substrate should not form a compound by reacting with the metallic film. However, Si wafer reacts with metal to form silicide, thereby interfering the single crystal growth of the metal film.
FIG. 1B shows another conventional process of manufacturing the single crystal metallic film. In FIG. 1B, in case that the single crystal substrate forms a compound by reacting with the metallic film, or the lattice mismatch is large, an intermediate layer 102 is employed. Such an intermediate layer 102 should have an epitaxy relation to the metallic film, and the lattice mismatch should be lowered.
Accordingly, the present invention is directed to a method of manufacturing a metallic film consisting of giant single crystal grains that substantially alleviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a method of manufacturing a metallic film consisting of giant single crystal grains having a grain size that has a ratio of thickness to an average grain size of the metallic film of more than 50.
Another object of the present invention is to provide a method of manufacturing a metallic film consisting of giant single crystal grains having a grain size that has a ratio of thickness to an average grain size of the metallic film of more than above 50, without depending upon the kind of substrate or deposition method.
Still another object of the present invention is to provide a method of manufacturing a metallic film consisting of giant single crystal grains having a grain size that has a ratio of thickness to an average grain size of the metallic film of more than 50, and having a uniform orientation.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve the objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a method of manufacturing a metallic film consisting of giant single crystal grains, comprises a first step of depositing the metallic film on a substrate at an atmosphere of an inert gas and a specified additive gas to change a surface energy, grain boundary energy, or internal strain energy of the metallic film, and a second step of annealing the resultant of the first step at a temperature suitable for carrying out a grain growth of the metallic film containing the additive gas.
For a better understanding of the present invention, a poly-crystalline metal or ceramic material system is considered. During an annealing process of the materials, a grain growth occurs to reduce the total energy of the material. The grain growth is caused by the reduction of the interface energy and internal strain energy depending upon a grain size. In case of a thin film, the grain growth is also caused by the anisotropy of the surface energy because of the very large surface area to volume ratio of thin film, together with the interface and strain energies. The decrease of the interface energy as a typical driving force for a grain growth may cause the grain growth to a grain size of 2 to 3 times the thickness. However, the anisotropy of the surface energy or the strain energy as the driving force may cause a portion of grains oriented to a specific direction to be selectively grown. As the thickness of the thin film becomes thinner, the anisotropy of the surface energy plays a greater role. Accordingly, an FCC metallic thin film may have a (111) preferred orientation. Meanwhile, it has been reported that if a large strain energy is applied to the metallic film according to the deposition condition, the selective grain growth having a (200) orientation occurred, to reduce the strain energy. However, by the conventional driving force, such as strain energy, only a limited number of grains are largely grown in the entire thin film, and the size of the large grain is limited.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.